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Guides - Configuration Options for NodeBalancers

Updated

Managed cloud-based load balancing service that provides high availability and horizontal scaling to any application.

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NodeBalancers, and load balancers in general, operate by taking inbound traffic over certain ports and distributing that traffic to pre-defined back-end instances. For NodeBalancers, the settings that accommodate this behavior are all stored within Configurations. Each configuration specifies the inbound port, the protocol, the load balancing algorithm, health checks, and the back-end nodes. This guide covers how to add or edit these configurations as well as the options that are available.

Add or Edit Configurations

Each configuration is assigned a single inbound port. Follow the instructions below to add or edit a configuration. If your application requires multiple inbound ports, create one configuration for each port you wish to use. This provides a great amount of flexibility, allowing each port to have its own distinct configuration settings and back-end nodes.

  1. Log in to Cloud Manager, click NodeBalancers in the left menu, and select the NodeBalancer you wish to edit. See Manage NodeBalancers.

  2. Navigate to the Configurations tab. This displays a list of all ports that have been configured.

  3. Open the port configuration you wish to edit or create a new one by clicking the Add Another Configuration button.

Configuration Options

Port

This is the inbound port that the NodeBalancer is listening on. This can be any port from 1 through 65534, though it should be set to whichever port the client software will connect to. For instance, web browsers use port 80 for HTTP traffic and port 443 for HTTPS traffic, though a client can change the port by specifying it as part of the URL.

Protocol

The protocol can be set to either TCP, HTTP, or HTTPS. While a brief description of each is provided below, review Available Protocols for more complete information.

  • TCP: Supports most application-layer protocols, including HTTP and HTTPS. This should be selected when you want to enable layer 4 load balancing, use TLS/SSL pass-through, use HTTP/2.0 or higher, balance non-HTTP services, or make use of Proxy Protocol. Since the NodeBalancer serves as a pass-through for these TCP packets, any encrypted traffic is preserved and must be decrypted on the back-end nodes.

  • HTTP: Unencrypted web traffic using HTTP/1.1. This terminates the HTTP request on the NodeBalancer, allowing the NodeBalancer to create a new HTTP request to the back-end machines. This can be used when serving most standard web applications, especially if you intend on configuring the NodeBalancer to use HTTPS mode with TLS/SSL termination.

  • HTTPS: Encrypted web traffic using HTTP/1.1. Since this terminates the request on the NodeBalancer, it also terminates the TLS/SSL connection to decrypt the traffic. Use this if you wish to configure TLS/SSL certificates on the NodeBalancer and not on individual back-end nodes.

    When using the HTTPS protocol setting, all traffic is decrypted on the NodeBalancer. Traffic between the NodeBalancer and the back-end nodes is sent over the private data center network, is not encrypted, and uses the HTTP protocol.

Proxy Protocol

When selecting TCP as the protocol, Proxy Protocol can be enabled to send client information to back-end nodes. Back-end nodes must also have Proxy Protocol enabled on supported applications to receive this information. There are two available versions of Proxy Protocol, v1 and v2:

  • v1: Proxy Protocol v1 adds a human readable string to all requests.
  • v2: Proxy Protocol v2 adds a more efficient binary data header to all requests.

For more information, see the Using Proxy Protocol with NodeBalancers guide.

Algorithm

The algorithm controls how new connections are allocated across the back-end nodes.

  • Round Robin: Allocates connections in a weighted circular order across the back ends.

  • Least Connections: Tracks each back end’s connection count and allocates new connections to the one with the least connections.

  • Source IP: Modulates the client’s IP to allocate them to the same back end on subsequent requests. This works so long as the set of back-end nodes doesn’t change, however the Session Stickiness setting (below) does affect this behavior.

Session Stickiness

This controls how subsequent requests from the same client are routed when selecting a back-end node. It allows a NodeBalancer to maintain a client session to the same back end.

  • None: No session information is saved and requests are routed in only accordance with the algorithm (see Algorithm above).

  • Table: This preserves the initial back end selected for an IP address by the chosen algorithm. Subsequent requests by the same client are routed to that back end, when possible. This map is stored within the NodeBalancer and expires after 30 minutes from when it was added. If a back-end node goes offline, entries in the table for that back end are removed. When a client sends a new request, it is then rerouted to another back-end node (in accordance with the chosen algorithm) and a new entry is created in the table.

  • HTTP Cookie: Requires the configuration protocol be set to HTTP or HTTPS. The NodeBalancer stores a cookie (named NB_SRVID) on the client that identifies the back end where the client is initially routed to. Subsequent requests by the same client are routed to that back end, when possible. If a back-end node goes offline, the request is rerouted to another back-end node (in accordance with the chosen algorithm) and the cookie is rewritten with the new back-end identifier.

    Note
    The client must have cookies enabled. If the client has disabled cookies or deletes cookies, session persistence is not preserved and each new request is routed in accordance with the chosen algorithm.

If session persistence is required or desired for the application, it is recommended to use both the Source IP algorithm in combination with either Table or HTTP Cookie session stickiness.

TLS/SSL Certificate and Private Key

When the HTTPS protocol is selected, the Certificate and Private Key fields appear and must be properly configured.

  • Certificate: The TLS/SSL certificate (and certificate chain) that has been obtained for the application.

  • Private Key: The passphraseless private key that is associated with the certificate file.

A certificate can be obtained for your domain by using certbot or by purchasing one through a trusted certificate authority. See TLS/SSL Termination for more details on obtaining a certificate and configuring both the NodeBalancer and back-end nodes.

Note
If you wish to use TLS/SSL pass-through and terminate the HTTPS connection on the back-end nodes, select the TCP protocol instead of HTTPS.

Health Checks

NodeBalancers perform both passive and active health checks against the back-end nodes. Back ends that are not responsive are marked as down and taken out of rotation.

Active Health Checks

Active health checks proactively query the back-end nodes by performing TCP connections or making HTTP requests. To enable an active health check, choose from one of the following types:

  • TCP Connection: Requires a successful TCP handshake with a back-end node.
  • HTTP Valid Status: Performs an HTTP request on the provided path and requires a 2xx or 3xx response from the back-end node.
  • HTTP Body Regex: Performs an HTTP request on the provided path and requires the provided PCRE regular expression matches against the request’s result body.

Additionally, configure the following settings to adjust the frequency and number of attempts:

  • Check Interval: Seconds between active health check probes.
  • Check Timeout: Seconds to wait before considering the probe a failure. 1-30.
  • Check Attempts: Number of failed probes before taking a node out of rotation. 1-30.

Passive Health Checks

The passive checks setting controls if passive health checks are enabled. When enabled, the NodeBalancer monitors all requests sent to back-end nodes. If the request times out, returns a 5xx response code (excluding 501 and 505), or otherwise fails to connect, the back end is marked as down and taken out of rotation.

Back-end Nodes (Compute Instances)

Load balancers work by distributing traffic to a pool of servers. For NodeBalancers, these servers are Linode Compute Instances and they are configured as back-end nodes. For information on configuring back-end nodes, see the Configure Back-end Nodes (Compute Instances) guide.

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